1. Field of the Invention
The present invention relates to an overlay measurement apparatus that performs an overlay inspection of each layer of a substrate in the manufacturing process of semiconductor devices, liquid crystal display devices, etc.
2. Description of the Related Art
An overlay measurement apparatus captures, for example, an image of each mark formed in an underlying layer and a resist layer of a substrate and finds an overlay displacement between the marks from the images, to perform an overlay inspection of each layer of the substrate. Further, To find an approximate value to an actual overlay displacement after etching processing, at the overlay inspection it corrects measurement error called WIS (Wafer Induced Shift) due to a substrate (for example, refer to Japanese Unexamined Patent Application Publication No. HEI 11-108626). WIS can be corrected by simple signal processing using a correction table created in advance.
The above-mentioned overlay measurement apparatus premises on an absolute stability of the manufacturing process. Because of this, a change in the manufacturing process due to a problem in processing conditions etc. makes it impossible to obtain an accurate overlay displacement even with the WIS correction. However, even when the problem occurs, the above-mentioned overlay measurement apparatus finds an overlay displacement through the same procedure without realizing the problem and regards it as accurate. This may cause a factor that reduces yield in the manufacturing process.